None.
Not Applicable.
1. Field of the Invention
This invention relates in general to a method of using load sensing devices and, more particularly, to a method of using uncalibrated load cell transducers to accurately weigh an object or quantity of material in a supporting structure subjected to variable stresses and distortions.
2. Description of Related Art
The prior art is generally dominated by devices which use or require calibrated load cell transducers. These calibrated load cell transducers are adjusted individually at the factory to provide the load cell transducers with uniform offset and sensitivity factors. However, calibration, testing, and specialized grouping of load cell transducers at the factory can raise the cost for manufacturing products incorporating the load cell transducers. To reduce this cost factor, previous devices have been invented which attempt to calibrate load cell transducers on products either after those products leave the factory or after the uncalibrated load cell transducers have been field-installed.
For example, U.S. Pat. No. 4,738,324 issued to Borchard, determines load cell offsets, scale factors, and the effects of structural flexure and distortion in the factory, and then programs unique calibration factors into each load cell transducer unit shipped. To accomplish this type of calibration, however, the load cell transducers must be installed prior to shipment from the manufacturer. This is impractical where the load cell transducers must be field-installed onto a storage device such as a grain bin or silo on a farm.
Similarly, U.S. Pat. No. 6,112,162 issued to Richards, attempts to solve this problem by performing an on-site calibration using multiple weights. Each weight is placed on top of each individual load cell transducer, effectively determining the scale factor for that individual load cell transducer. This is repeated for each of the individual load cell transducers, resulting in an awkward and time consuming operation. Variations on this type of invention are additionally disclosed in U.S. Pat. No. 5,805,467 issued to Richards and U.S. Pat. No. 5,724,267 also issued to Richards.
Other patents disclose various methods for calculating weights within or upon flexible structures. Examples of such methods are disclosed in U.S. Pat. No. 6,069,324 issued to Shimizu, et al., and in U.S. Pat. No. 6,209,382 issued to Komata, et al. However, in each of these cases, the method depends upon the use of load cell transducers which have been previously calibrated. As such, these methods are again relatively costly.
Accordingly, there is a need to overcomes these and other problems by providing a method by which lower cost uncalibrated load cell transducers and load sensing devices can be field-installed on flexible structures while still providing the ability to provide accurate weight measurements of substances within the flexible structure.
The present invention resides in a method for performing a calibration process to field-calibrate uncalibrated load sensing devices and load cell transducers. The calibration can be performed when only two known weight conditions exist. The method compensates for load cell offset, scale factor differences between load cells, and flexure or stresses in the structure supporting the weight.
More specifically, this invention is a method for automatically calibrating a set of uncalibrated load cell transducers supporting a variable load whose weight is distributed in some unknown and variable way among the load cell transducers. The calibration method compensates not only for the varying offset and scale factors for the individual load cell transducers, but also compensates for the variable weight distribution on the load cell transducers due to warping and flexibility in the structure supporting the weight and load cells.
The present invention also resides in embodiments of the above invention, including the generation of software which allows for the input of the uncalibrated load sensor and load cell transducer readings and which can process the mathematics of the equations described herein.
Therefore, it is an object of the invention to provide a method which permits the use of less expensive uncalibrated load sensing devices or load cell transducers by calibrating the load cell transducers through a procedure after field-installation. In addition, this method automatically compensates for the unknown and variable distribution of the weight among the several load cells used to measure the weight.
It is yet another object of the invention to provide a method to monitor the weight in any tank, bin, or other structure holding a variable weight where an inexpensive means to monitor weight is required.